Tone control



Patented Jan. 5, 1937 UNITED :STATES PATENT OFFICE TONE CONTROL Application August so, 1930, Serial No. 478.832. Renewed September 21, 1933. In the Netherlands September 25, 1929 13 Claims.

The presentinvention relates to audio control systems, and more particularly to improvements in, or relating to, sound-reproducing devices.

With sound reproducing devices in which electric currents are converted into sound vibrations,

it has hitherto always been tried to make the sound reproduction as faithful as possible. This faithfulness has been sought after by making, in the sound reproduced, the ratio of the intensities of the different tones in physical respect the same as in the original sound. With these devices it is often desired to amplify or to attenuate the sound reproduced. This is efiected with the socalled volume control. This volume control has, hitherto, been realized in such a manner that with the aid of a controlling member the physical strength of all tones, or pitches, was increased or decreased in substantially the same measure.

The present invention is basedon the view that one must not first of all try to obtain fathfulness in the sense above referred to, but that one should try to effectuate the volume control in such manner that the attenuation, or amplification, of the sound reproduced does not alter its character as it is physiologically perceived. The importance thereof may be elucidated by referring to a very simple exposition given hereinafter.

As is well known, the human ear is not equally sensitive'to all frequencies'located in the zone of audibility. The sensitiveness of the ear is greatest for frequencies lying in the neighborhood of 1500 to 2000 cycles, while upwards and downwards the sensitiveness gradually decreases. Besides, there exists a so-called threshold value which is dependent on the frequency, and which is lowest for those frequencies to. which the ear is most sensitive. For the very high frequencies, as well as for the very low ones, the threshold value is very high. By the term threshold value is meant the physical intensity required to produce a just perceptible sounding impression.

The curve representing the threshold value in dependency on the frequency has a minimum in the neighborhood of the frequency 1500 .to 2000, and gradually rises both on the high and on the low side. With a given sound, in which in addition to the tones of the middle register also occur the high and the low tones, it may occur that when all the tones are uniformly attenuated the high and the low tones obtain an intensity-lying below the threshold value, owing to which-the character of the sound would be altered. -The character of the sound must be understood: to

mean the physiologically perceived ratio-0f iii-- tensity of the different tones.

If the sound consists, for example, of two single tones whose physical intensities are A and B, the physiological impressions of the intensities of these two tones will be quite different, and may be represented by the numbers C and D. Now the ratio between C and D determines in the above mentioned sense the character of the sound perceived. The present invention consists in the use of means for keeping the said ratio C D at any rate approximately constant independently of the absolute intensity; consequently, of the intensity measured with a physical measure. That which is said here also applies, of course, to sounds of more composite nature.

The device, according to the present invention, may be utilized in conJunction with the ordinary volume control with which the intensity of all tones is altered in substantially the same measure.

The inconvenience particularly prevalent with wireless sets, consisting in that together with the intensity of the sound its nature is also altered in the sense as above defined, is eliminated thereby. Many users of receiving sets, who do not exclusively aim at obtaining the highest possible sound volume, regulate the intensity of the sound until the total impression is a pleasant one. In this case, however, the intensity is often insufficient if the listeners are at some distance from. the reproducing device. With the ordinary apparatus the quality of the sound is modified by increasing its intensity. By employing the device, according to the present invention, this in-' convenience is entirely eliminated, and after, for example, the intensity has first been increased with the ordinary volume control, it is possible to get back the original quality.

A simple means of maintaining constant the said physiological character of the sound consists in connecting an impedance in parallel with the primary, or with the secondary, winding of a transformer acting as a coupling element between two subsequent amplification stages of an amplifier, said impedance being constituted by the series-connection of an inductance and a. capacity in parallel with a resistance which may be constructed as a potentiometer. Thedevice functions as follows: If the intensity of a given sound is altered with the aid of a known volume control- ,ling device its physiological character will be modified. Displacement of the potentiometer contact permits the restoration of the original quality impression.

The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claims, the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawing in which I have indicated diagrammatically several circuit organizations whereby my invention may be carried into effect.

In the drawing:

Fig. 1 shows one embodiment of the invention,

Fig. 2 illustrates a modification,

Fig. 3 shows still another modification.

In Fig. 1, I represents a thermionic valve acting as an amplifier in an ordinary electric lowfrequency amplifier. In the anode circuit of the valve is included the primary winding 2 of a transformer whose secondarywinding 3 is connected to the grid and the filament of a succeeding thermionic valve 5. In parallel with the primary winding of the transformer is connected an impedance consisting of a resistance 6 on the one side, and a resistance 1 in series with a capacity C and an inductance L on the other side.

The impedance, consequently, consists of two parallel branches 6 and I, C, L. The resistances 5 and I may be combined so as to form a single potentiometer resistance, a variable point of which is connected, for example, by means of a sliding contact 9 to one of the terminals of the primary winding 2. If the resistance 6 is small, in comparison to the resistance 1, the final sound will be relatively faint. When the value of the resistance 6 is gradually increased, the sound will be amplified, as long as the value'of the resistance 6 is still small, relative to the ohmic resistance in the branch 1, C, L, in such manner that the physical intensities of all frequencies increase in' the same measure.

If, however, the resistance 6 has a high value, the alternating current resistance of the branch I, C, L will be relatively small for those frequencies which are located in the neighborhood of the resonance frequency of the circuit which may be formed with the elements L and C. The result thereof is that the frequencies lying in the neighborhood of the resonance frequency, are amplified comparatively less than the frequencies which are higher or lower than the said resonance frequency.

It has been found that thus a volume control is obtained which allows of regulating at will, and independently of the intensity, the character of the sound. It is evident that instead of a single L, C combination, it is also possible to connect a plurality of such combinations in parallel, in which event the resonance frequencies of the various L, C combinations may be different. Fig. 3 shows a plurality of L, C combinations in parallel, the series combination of C1 and L1 being connected in shunt with the combination C, L.

The degree of damping of the L, C circuit determines the width of the minimum in the frequency characteristic curve of the device. Very satisfactory results are obtained by using the following values: Internal resistance of tube I equal to ohms; resistance of resistor l resistor 6 equal to 11.10 ohms. If the resistance of the part 1 is considerably smaller than the internal resistance of the valve, and, if at the same time resistor i is larger than the internal resistance, the frequency characteristic curve shows a "pit the situation of which is determined by L and C. The total amplification slightly decreases, but this decrease is amply compensated by the gain in quality. If, for example, the value of the resistance 8 is substantially equal to the internal resistance, and if, at the same time, the value of the resistance 1 is larger than the internal re sistance, the average amplification of all frequencies will still be 50% of the maximum value.

It is evident that the above described volume control can also be utilized in the secondary circuit of the transformer 3, in which event one obtains the circuit-arrangement represented in Fig. 2, similar conventional symbols and reference numerals representing the same elements.

The operation of this circuit arrangement distinctly appears from the drawing, and needs no further explanation.

While I have indicated and described several systems for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and described, but that many modifications may be made without departing from the scope of my invention as set forth in the appended claims.

What I claim is:

1. In combination, in an audio amplifier, at least a pair of electron discharge tubes, a coupling means between the input circuit of a succeeding tube and the output circuit of a preceding tube, a resistor in shunt with said coupling means and including means for adjustably connecting a point of high audio frequency potential of said coupling means to said resistor, a series resonant path, including an inductance and capacity, connected in shunt with said resistor.

2. In combination, an electron discharge tube, a succeeding load circuit, an audio'transformer coupling the output circuit of. said tube and said load circuit, and a combined volume and tone control means comprising an impedance across one of the windings of said transformer, and a series resonant path connected in shunt with said impedance, there being an adjustable connection between a high potential point of said winding and said impedance.

3. In combination, an electron discharge tube, a succeeding load circuit, an audio frequency transformer coupling the output circuit of said tube and said load circuit, a network including a resistor in parallel with a series resonant path, said network being connected in parallel with one of the windings of said transformer, the connection between one of the terminals of said last mentioned transformer winding and a desired point of said resistor being adjustable.

4. In combination, an electron discharge tube, a succeeding load circuit, an audio frequency transformer coupling the output circuit of said tube and said load circuit, a network including a resistor in parallel with a series resonant path, said network being connected in parallel with one of the windings of said transformer, the connection between one of the terminals of said last mentioned transformer winding and a desired point of said resistor being adjustable, and said series resonant path being resonant to a frequency to which the human ear is most sensitive.

5. A manually operable volume control device for an audio frequency amplifier of. the type including at least two tubes and an audio frequency transformer coupling the output circuit of one tube to the input circuit of the second tube, said device consisting of a variable resistor in shunt with one of the transformer windings, and a reactive path connected in shunt with the resistor including a condenser and inductance in series, said path having a resonant frequency located in the vicinity of the audio frequencies to which the human ear is most sensitive.

6. A manually operable volume control device for an audio frequency amplifier of the type including at least two tubes and an audio frequency transformer coupling the output circuit of one tube to the input circuit of the second tube, said device consisting of a variable resistor in shunt with the transformer primary, and a reactive path connected in shunt with the resistor including a condenser and inductance in series, said path having a resonant frequency located in the vicinity of the audio frequencies to which the human ear is most sensitive.

7. A manually operable volume control device for an audio frequency amplifier of the type including at least two tubes and an audio frequency transformer coupling the output circuit of one tube to the input circuit of the second tube, said device consisting of a variable resistor in shunt with the transformer secondary, and a reactive path connected in shunt with the resistor including a condenser and inductance in series, said path having a resonant frequency located in the vicinity of the audio frequencies to which the human ear is most sensitive.

8. In combination, a tube, a succeeding audio frequency amplifier tube, an audio frequency transformer coupling the output circuit of the first tube to the input circuit of the amplifier tube, a resistor, means connecting one terminal of. the resistor to the low potential side of the transformer primary, an adjustable tap connecting the high potential side of the primary to an intermediate point of the resistor, and a path, including a condenser and coil connected in series, having one terminal connected to the said low potential terminal of the resistor, the opposite terminal of the path being connected to th high potential terminal of the resistor.

9. The combination with an audio frequency signal transmission circuit, of a volume control potentiometer device connected in shunt relation to said circuit, an audio frequency output circuit connected to a movable tap and one terminal of said potentiometer device, and a tone compensating circuit permanently connected to a second tap and one terminal of said potentiometer device and having an impedance less than that of said potentiometer at a predetermined audio frequency.

10. The combination with an audio frequency signal transmission circuit of a volume control potentiometer device having an impedance element connected in shunt to said circuit, anaudio frequency output circuit connected to a movable tap and one end terminal of said impedance element, and a tone compensating circuit, including means for attenuating audio frequency signals within a certain frequency range, permanently connected to a second and fixed tap on said impedance element and said one terminal thereof.

11. In combination with a source of audio frequency energy and an audio frequency utilization load, a connection between said source and load including a volume control element, consisting of a resistor and adjustable tap, connected in shunt with said source and load, and a reactive path, resonant to a desired frequency of the useful audio range, permanently connected in a shunt relation to said resistor, whereby adjustment of said tap in one direction results in an attenuation of said desired frequency, said load being connected to said resistor solely through said tap.

12. In combination with a source of audio frequency energy and an audio frequency utilization load, a connection between said source and load including a volume control element, consisting of a resistor and adjustable tap, connected in shunt with said source and load, and a reactive path, resonant to a desired frequency of the useful audio range in the vicinity of 1500 to 2000 cycles, permanently connected in a shunt relation to said resistor, whereby adjustment of said tap in one direction results in an attenuation of said desired frequency, said load being connected to said resistor solely through said tap.

13. In combination, a tube, a succeeding audio frequency amplifier tube, an audio frequency transformer coupling the output circuit of the first tube to the input circuit of the amplifier tube, a resistor, means connecting one terminal of the resistor to the lowpotential side of the transformer primary, an adjustable tap connecting the high potential side of the primary to an intermediate point of the resistor, and a path. including a condenser and coil connected in series, having one terminal connected to the said low potential terminal of the resistor, the opposite terminal of the path being connected to a point on the resistor which has a higher potential than said low potential resistor terminal.

POPKO REINDER DYKSTERHUIS. 

